size group; gel batteries as much as five times the price. AGM and gel VRLA batteries: Have shorter recharge time than flooded lead–acid batteries. Cannot tolerate overcharging: overcharging leads to premature failure. Have shorter useful life, compared to properly maintained wet-cell battery. Discharge significantly less hydrogen gas. AGM batteries are by nature, safer for the environment, and safer to use. Can be used or positioned in any orientation. See also Gaston Planté List of battery types Rechargeable battery Sand battery References Further reading Books and papers Valve-Regulated Lead-Acid Batteries. Edited by Patrick T. Moseley, Jurgen Garche, C.D. Parker, D.A.J. Rand. p202 Vinal, G.W. (1955 Jan 01) Storage batteries. A general treatise on the physics and chemistry of secondary batteries and their engineering applications. Energy Citations Database (ECD) : Document #7308501 John McGavack. The Absorption of Sulfur Dioxide by the Gel of Silicic Acid. Eschenbach Print. Company, 1920. Patents – Treatment Of Porous Pots For Electric Batteries. Erhard Ludwig Mayer and Henry Liepmann – Solid Acid Storage Battery Electrolyte. Alexander Koenig et al. – Composite battery plate grid – Lead acid battery plate with starch coated glass fibers – Method of making a lead storage battery and lead storage battery made according to this method. Otto Jache's and Heinz Schroeder External links Why do I need a special battery for the automatic start-stop system?, published by Varta Pros and cons of AGM batteries, published by Lifeline Lead Rechargeable batteries Sulfuric acid